Many companies do not supply references for former employees. The policy is to verify that the person was employed there, and optionally, give their job title.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
This letter is in response to your request for employment references for <name>. It is our company policy not to give such references, but simply to verify employment. <name> was an employee at Abc Company from <start date> to <end date>. <Optional job title.>